Lightweight trolling motor battery

[Jim McC]

I'm wondering what you guys are using as a lightweight battery, for a trolling motor in your kayak ? My motor is a 40 lb. thrust model.

 

Thanks.  

[Jim McC]

No one has a recommendation ?

[Born 2 fish]

Pick any of the expensive lithium batteries:

[MN Fisher]

A 40# thrust TM will take about 40amps of power to run at full speed - that's 40AH for an hour of travel time. Running at minimum speed it still takes about 5amps - so 5AH for an hour.

 

A Sealed Lead-acid battery of 100AH will run under $200 and weigh about 60lbs

A Lithium battery of 100AH will weigh under 30lbs - but they start at around $800

 

So, affordable or lightweight - can't have both.

[Way2slow]

Other than Lithium, the weight is going to depend on how much you plan to use it and how long.   Weight depends on run time, the more runtime you want, the more lead the battery will have.  The more lead, the more weight. If you only plan to go for a few hours and don't plan to do much max thrust running, a lower capacity group 24 will work just fine.  Running on max thrust with a 12V TM, is extremely inefficient and will use up a battery quickly.  

The lighter the battery you want, the more efficient the TM you should have.  That means using a digital and not one of those with the five or so set speeds.  Huge difference in run time when you are just easing along and not trying to run max thrust. 

I would think some of the plastic boat guys with experience with them would have some suggestions since it really does not take a lot the move on of those things around.

[Jim McC]

Thanks guys

[Bankc]

Also, keep in mind that with a lead acid type battery, you don't want to run it down below about 50%.  So you'll need double the size of battery of what you plan to use if you go that route.  Lithium batteries don't seem to mind being  drained deeply as much, so you can get by with a lithium battery with about the 75% the amp-hour rating as what you'd use for a lead acid type under the same conditions.  So theoretically, a 60lb, 100AH lead acid battery is going to be about as effective for you as a 25lb 75AH, lithium battery.  

 

Personally, I just use a regular 100AH deep-cycle lead-acid.  I bought it for about $100 at Autozone.  It weighs 60lbs and is huge!  I have to launch the kayak into the water first and then install it, because I can't balance it on the cart with that battery loaded.  Plus, it puts a lot of weight in the rear of my kayak, and causes the bow to lift about an inch.  It's not ideal, but I can live with it.  My plan is to run that one into the ground, and then when it's time to replace it, check out the prices on lithium batteries again.  Right now, they're too expensive to be worth it for me.  In a few years, they will likely be more reasonable.  There's even a chance that going this route might actually save me money in the long run.  The price of a big lithium battery only has to drop $100 over the next few years for me to break even.  With the nature of technology these days, that's not a ridiculous gamble.  

[Jim McC]

Good info Bankc. Thanks.

[Born 2 fish]

I use a Duracell 31 deep cycle for my 55lb thrust and it’s heavy but I want as much reserve as possible. 

[Goose52]

I run either a 45 or 55lb thrust TM on my 12' canoe. I previously used a Group 24 lead-acid battery (about 70AH) which weighed about 53 pounds when in a Minn-Kota power center box.  As mentioned in a post above, lead-acid batteries don't like being discharged to a very low level but I still had all the power I needed to spend an 8 or 9 hour day on the water (albeit mostly all at low speeds with few if any full-power runs).

 

After watching the technology mature for a number of years, I finally got on the lithium bandwagon at the beginning of this season, purchasing a 100AH lithium-iron "Ionic" branded battery from these guys:  https://lithiumhub.com/   Since lithium batteries can be discharged fairly deeply without ill affect, I considered getting the 12v 50AH model but with an abundance of caution I ended up getting the 100AH model.  I now have about twice the "usable" AH capacity and my weight is down to around 30 pounds with the battery in that MK power center box. I can make 4 half-day trips on the water and still have around 50% capacity left in that 100AH model. So, as it turns out, I could have done nicely with that 50AH battery and if I could have a "do-over" I would certainly get that model and still have plenty of capacity for long days on the water. The 50AH battery is listed as weighing only 14.3 pounds with dimensions of 6.5″ x 7.7″ x 7.0″ and would be a great candidate for your yak.

 

This particular brand of battery is bluetooth enabled and you can install an app on your phone that will let you track your battery capacity, charge status when on the charger, and a bunch of other parameters. This app and bluetooth interface has worked flawlessly for me.

 

More info is available on the listed web site...

[Smalls]

The entry price of lithium may seem steep, but keep in mind you'll get 4-5x + the longevity of lead acid. A lead acid might be good for 4-500 cycles if you take care of it well. You can get well over 2000 cycles out of lifepo4. 

[Smalls]

On 8/25/2020 at 8:04 AM, Goose52 said:

 

This particular brand of battery is bluetooth enabled and you can install an app on your phone that will let you track your battery capacity,

This is an extremely valuable feature. Voltage meters for lead acid batteries won't be accurate with lifepo4, and the correct meters are often over $100.

[DogBone_384]

37 minutes ago, Smalls said:

Voltage meters for lead acid batteries won't be accurate with lifepo4

?????

[Bankc]

1 hour ago, DogBone_384 said:

?????

I think he means that voltage meters designed for lead acid type batteries won't be accurate with Lithium Iron Phosphate (LiFePo) batteries, which is the type of Lithium battery used for trolling motors.  LiFePo4 batteries have a very flat discharge curve, so they'll pretty much read a steady voltage until right before they die.  The discharge curve on Lead Acid is closer to linear, making a standard voltage meter style gauge easier to use to measure remaining capacity.  To get a good idea of the life left in a lithium battery, you have to have a device capable of constantly measuring and recording the amperage draw as well as the amount of time that the draw occurred over.  In other words, it has to measure the actual amps and hours to get the AH remaining, versus just taking a voltage reading to infer the AH remaining.  

[Smalls]

3 hours ago, DogBone_384 said:

?????

What Bankc said. Here's a chart showing just how flat the discharge is. 

[Goose52]

I'm glad you guys answered that question so well !   And yes, when I was running the lead-acid battery, I would watch the voltage reading showing on my sonar screen drop from the 12v range, down into the 11s, and on a long day, even into the high 10 volt range - that was my only indication of my remaining battery capacity.

 

With this lithium battery and the associated bluetooth app, I can pull up these three screens on my phone and know just about everything going on with that battery. Is all this data absolutely necessary to have? No. Is it very handy to have? Yep.

 

(Images copyright of Lithiumhub.com - from their web site here:  https://lithiumhub.com/product-information/ionic-batteries/bluetooth-guide/   Disclaimer - I have no relationship with these guys other than as a customer!)

 

 

[N Florida Mike]

I dont know about all this^^^^^
 I just use a 12 volt deep cycle battery with my 40 pt and it works fine. But that’s in my JBoat. Probably weighs around 50 pounds.